Group 13: the boron group

Three outer electrons: ns² np¹

Each configuration ends in ns² np¹, as in boron ([He] 2s² 2p¹) and aluminum ([Ne] 3s² 3p¹). Aluminum, gallium and indium lose all three to form Al³⁺, Ga³⁺ and In³⁺. Removing three electrons from tiny boron would cost too much energy, so it shares them instead; in boron trifluoride (BF₃) it has only six electrons around it and readily accepts another pair.

At the bottom, thallium prefers +1. Its pair of 6s electrons tends to stay out of bonding, so Tl⁺ is more stable than Tl³⁺.

Trends down the group

Boron is a hard, dark metalloid that melts at 2349 K, but the metals below melt far lower: aluminum at 933.47 K, gallium at only 302.91 K, about 30 °C, indium at 429.75 K and thallium at 577 K. Density climbs steadily from 2.34 g/cm³ for boron to 11.85 g/cm³ for thallium.

One surprise: gallium’s electronegativity, 1.81, is higher than aluminum’s 1.61. The ten d electrons that gallium gains on the way across the transition metals shield its outer electrons poorly, so its nucleus holds them more tightly than you might expect.

Where you meet group 13

Aluminum is the most abundant metal in Earth’s crust and turns up in drink cans, foil, window frames, aircraft and power lines; recycling a can takes only a small fraction of the energy needed to make new aluminum. Boron is in borosilicate glass for ovenware and lab glass, and in borax cleaning powder. Gallium nitride lets LEDs shine blue and white, and indium tin oxide makes touchscreens conduct. Thallium is highly toxic and has few uses.

Nihonium

Nihonium (113) was the first element discovered in Asia, at the RIKEN laboratory in Japan, and its name comes from Nihon, a Japanese name for Japan. Only a few atoms have been made, so its properties are predicted, not measured.